Endoscopes have attained great acceptance within the medical community, since they provide a means for performing procedures with minimal patient trauma, while enabling the physician to view the internal anatomy of the patient. Over the years, numerous endoscopes have been developed and categorized according to specific applications, such as cystoscopy, colonoscopy, laparoscopy, upper GI endoscopy and others. Endoscopes may be inserted into the body's natural orifices or through an incision in the skin.
An endoscope is usually an elongated tubular shaft, rigid or flexible, having a video camera or a fiber optic lens assembly at its distal end. The shaft is connected to a handle, which sometimes includes an ocular for direct viewing. Viewing is also usually possible via an external screen. Various surgical tools may be inserted through a working channel in the endoscope for performing different surgical procedures.
There are known various endoscopes employing in their front insertion part, optical heads for viewing the interior of a body cavity or lumen such as the lower digestive track. Such optical head normally includes at least an illumination means for illuminating the object, an objective lens system and a sensor array.
U.S. Pat. No. 6,956,703 discloses an objective lens for endoscopes comprises a front lens unit component and a rear lens unit component, between which a aperture stop is located, wherein the front lens unit component comprises, in order from the object side, a first lens having a negative refractive power, and a second lens having a positive refractive power which directs a surface of the small radius of curvature toward the object side; wherein the rear lens unit component comprises a third lens having a positive refractive power which directs a surface of the small radius of curvature toward the image side, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power; and wherein the fourth lens and the fifth lens are cemented. The following condition is satisfied: 2.0<|f3/f|<3.0 where f is the composite focal length of the total system and f 3 is the focal length of the third lens. Still, the complexity of the objects that are inspected by the endoscope (for example, the asymmetric colon environment), requires high quality images capturing a wide Field of View (FOV), which cannot be accomplished using only one detector.
More efforts have been undertaken to improve the optical design of these systems and to create a wide FOV, as seen for example, in U.S. Pat. No. 5,870,234 entitled “Compact wide angle lens”, as well as U.S. Pat. No. 6,476,851 entitled “Electronic endoscope”. Although these patents bring the advantage of a wide FOV they mainly provide a front view. Another disadvantage is a significant distortion in the periphery looking at the borders of the wide view image.
These disadvantages may be partially solved by using a multi image lens for example as shown in US patent application number 2005/0168616 entitled “Methods and apparatus for capturing images with a multi-image lens” or by using other Omni-directional optical solutions, as disclosed, for example, in U.S. Pat. No. 7,362,516 entitled “Optical lens providing Omni-directional coverage and illumination”. These technologies may support a wide FOV with relatively low distortion in the periphery of the image however they suffer from a major disadvantage of low optical resolution on side views. Another disadvantage of these technologies is the complexity and space consuming design which typically eliminates the possibility to combine other crucial features like jet, working channels and illuminating sources to the endoscope.
There is still a need in the art for endoscopes, such as colonoscopies, that provide a wide FOV, a wide range of Depth of Field/Depth of Focus (DOF) and acceptable resolution within the required dimensions of the device used of a medical application.